Florida’s segregated juvenile justice system, “Harlem Shuffle” is a wildly entertaining romp. But as you might expect with this two-time Pulitzer Prize winner and MacArthur genius, Whitehead also delivers a devastating, historically grounded indictment of the separate and unequal lives of Blacks and whites in mid-20th century New York.Like a lot of heist novels, the plot is twisty, with a large, at times bewildering cast of characters and a few storylines that border on the ridiculous.